REMEMBER the big nitrite scare of two years ago? (No more bacon or hot dogs or other cured meats because nitrite additives in the meat "cause cancer.") Well, it now turns out that the study that seemed to show this was incorrect. At the moment there is no evidence that nitrites in the diet cause cancers of the lymphatic system or of other system.

However -- sad to say -- that does not mean that the subject is closed, or that there aren't lots of scientists who are still uneasy about nitrites. The reason is that nitrites can be converted during cooking, or by natural processes inside the body, to chemically related substances known as nitrosamines. Nitrosamines are known to cause cancer in a number of different types of animals. Though they have not yet been proven to cause cancer in man, it would be unusual if such a potent animal carcinogen were inactive in humans.

It isn't yet known how much of the nitrosamines inside the body origianlly come from nitrite-treated meats: it may turn out to be a very small proportion. First of all, nitrites are produced in the body by intestinal bacteria that make them from -- bear with us -- nitrates. Many vegetables have high concentrations of nitrates; so does some drinking water. And there are many other routes of exposure to nitrosamines. Cigarette smoke has a lot, as do agricultural herbicides and many women's cosmetics. Even new car interiors have relatively high levels.

Where does all this leave government regulators? While nitrites do not have an absolutely clean bill of health, they do now seem to rank very low on the long list of toxic chemicals, new drugs, environmental pollutants, food additives and other substances that need investigating. It is therefore unlikely that we will hear anything more about a nitrite ban unless unexpected new evidence turns up.

And where does it leave the bewildered layman -- who is accustomed to thinking of scientific research as a slow, but steady march toward the truth but who recently has seen it lurching back and forth in an apparent state of complete confusion? The answer is that science only looks like an orderly process from a distance. Textbooks may make it look as if Pasteur or Curie or Newton went from A to B to C and right ahead to the answer, but the usual progress is more like: E to B to C to R to A. This holds not only for individual experiments, but also for entire fields as they develop. Only after a crucial idea is proposed does a mass of apparently contradictory data all of a sudden make perfect sense. Cancer research and the broader field of toxicology -- the study of how substances may harm the body -- are in just such an early, messy, confusing stage and are likely to stay that way for some time.

Non-scientists aren't usually privy to all this confusion. But the Freedom of Information Act and post-Watergate supersensitivities about cover-ups face the government regulator with a whole new dilemma. The scientist in him may want to wait for a second study to confirm the first before making any public announcements, but the public servant knows that this is impossible, especially if it's going to take years to get the necessary answers. Our let-it-all-hang-out style of government has it pluses and minuses.This is one of the minuses: the public is going to have to get used to living with a new and unsettling degree of uncertainty -- about nitrites and, sooner or later, almost everything else.